The present invention relates to improvements in papermaking machinery and, more particularly, to a paper web winder wherein a continuous traveling web material, such as paper, is wound onto a core and into a wound web roll.
In high speed winding of a web, such as paper web being wound into a roll, the web is conventionally started on a core and the roll wound on the core is supported and driven in rotation. The support is frequently provided by two horizontal winding drums. One or both of the drums are driven in rotation and the approaching web winds over one of the drums onto the winding roll at relatively high speeds, frequently substantially in excess of 4,000 feet per minute. It is imperative that winding the web onto the winding roll progress uniformly so as to maintain a constant tension of the web on the roll and to insure that the wound web roll is uniform. Uncontrolled progression of the winding can result in non-uniform tension of the web on to the roll and distortions in surface quality and non-uniformity of the cylindrical shape and density of the roll. It is also necessary to control the high speed of rotation of the winding so as to mitigate or eliminate vibration and the winding roll must be maintained controlled in the pocket between the winding drums.
One factor in maintaining control and quality of the roll being wound is to apply a downward force on the winding roll which affects the nip pressure between the roll and the supporting drums. The force also must be applied in a manner so that the vibration and hopping or bouncing of the roll, or other forms of vibration, do not occur. It is necessary to take into consideration several factors, such as any lack of control of the nip pressure between the supporting drums and the roll; holding the roll positioned in the pocket so that the speed of the roll surface will not change; the size of the roll and its weight will change very substantially during the winding process. The high speed rotation of a roll of substantial size and weight as the roll being wound is very difficult to control, and vibration or bouncing are two modes of disturbances which should be avoided.
These modes are characterized by repetitive radial motion, sometimes called buzzing, against a winding drum, which affects wound roll speed and quality. Another adverse effect is rocking, which takes the form of repetitive angular motion alternating in direction along an arcuate path, sometimes known as thumping, which occurs with respect to the winding drum. This is a less frequent problem than the radial motion. The bouncing or vibration of the paper roll in a double drum winder wherein the roll is supported on two parallel drums is a cause for reduced production during the winding operation.
The paper maker observes the problem as audible buzzing or a rocking thumping back and forth on the winding drums. He will attempt to adjust tension on the web or pressure of the rider roll on top of the wound roll to control the bouncing, generally with little success. It then becomes necessary to reduce speed until the buzzing or thumping is controlled. This vibration or bouncing not only causes production difficulties requiring slowing of the winding process, but it also creates maintenance problems. As to the mechanism itself, looseness of parts will occur, foundation cracks and excessive wear and fatigue of the metal of parts can occur.
This operation with accompanying bouncing can also be extremely dangerous to personnel in the vicinity of the winder because of the high kinetic energy of a roll rotating at over 4,000 feet per minute when the roll weighs several thousand pounds. This disturbance in the roll continues to be generated around the circumference of the roll until it closes to form a repeating cycle. Thus, the bouncing becomes a harmonic of the wound roll rotation. The initial disturbance may be caused by many factors, including uneven paper surface, machine direction basis weight variations, caliper variations, eccentric starts, variations in paper or paper-to-steel frictional characteristics, glue, unwinder drums and winder chevrons. Once this disturbance occurs, the next disturbances which follow are related to the energy available or the deformable nature, diameter and roll characteristics (friction) of the wound roll.
Adjusting web tension or rider roll pressure is in effect an attempt at changing the deformable nature of the paper roll. It is difficult to have much control over the problem by making these adjustments. A poorly wound roll is generally the only result.
The amount of web tension wound into a paper roll is affected largely by rolling nips on the outside of the paper roll during the winding process. In a conventional two drum winder there are three of these rolling nips, one at each drum, and one at the rider roll. The amount of tension induced is a function of the nip force and an inverse function of the radius of curvature of the nipping roll or drum. A hard nip, such as provided by a steel roll, induces more tension than a softer nip, such as provided by an elastomeric tire or an unsupported belt.
To produce a roll of paper with good internal structure, it is necessary to induce high tension in the paper roll when winding is first started on the core, and then reduce that wound-in tension as the roll builds up to its final diameter.
Reducing the rewinding roll speed generally reduces the tendency for the initial disturbance to deform the roll, and it reduces energy available to sustain the vibration. It is also a means of reducing or stopping winder bounce, but does not, of course, result in being able to maintain production speeds.
The two drum winder actually presents a mass elastic system which can be envisioned as consisting of a rotatable mass having deformable springs on fixed drums. That is, the reaction force between the supporting drums and the roll is resilient in nature, having a spring constant. With this, the natural frequencies can be calculated. These natural frequencies change with change in roll size. The rider roll engaging the top of the wound roll provides another force relationship which interacts with the spring constant. Thus, the resiliency of the roll engaged at three points of support, i.e., the two supporting drums, and the rider roll, can provide an unstable unit when operating at high speeds.
Efforts to control bouncing have included adding a vibration absorber to the rider roll, but this has not proven to fully solve the problem.